1. Field of the Invention
The present invention relates generally to ion implantation and, more particularly, to a sputter enhanced ion implantation process that uses to advantage the ion beam sputtering phenomenon for forming layers of coatings on surfaces of interest simultaneously with ion implanting that surface.
2. The Prior Art
Ion implantation is a well known process. As known, ion implantation improves the physical and chemical properties of the surfaces of workpieces, such as razor blades and surgical instruments. See U.S. Pat. No. 3,900,636 entitled "Method of Treating Cutting Edges." See also U.S. Pat. No. 3,925,116 entitled "Superhard Martensite and Method of Making the Same." Of particular interest has been the ion implantation of workpieces, such as surgical orthopaedic implants, made from titanium and its alloys, see U.S. Pat. No. 4,465,524 entitled "Titanium and its Alloys." While effectively improving the wear performance of titanium-alloy surgical implants, ion implantation thereof has caused the surfaces of the implants to discolor at spots. In a recently granted U.S. Pat. No. 4,693,760 of mine entitled "Ion Implantation of Titanium Workpieces Without Surface Discoloration," it is noted that the discolorations on the ion implanted workpieces are sputter deposited thereon from parts located within the workpiece handling endstation due to sputtering by the ion beam. By preventing undesirable sputtering occasioned by ion implantation, the process of my U.S. Pat. No. 4,693,760 has achieved its stated objective. The disclosure and teachings of my said U.S. Pat. No. 4,693,760 are incorporated herein by reference. In a copending and related application Ser. No. 167,632, filed Mar. 11, 1988, entitled "Method and Apparatus for the Ion Implantation of Spherical Surfaces," Group Art Unit 111, and assigned to a common assignee with this application, to wit, Spire Corporation of Bedford, Mass., the adverse undesirable effects of sputtering during ion implantation also have been recognized and dealt with. Other workers in the field also have described the significance and adverse effects of sputtering experienced during the ion implantation of components for wear and corrosive protection. See F. A. Smidt et al, "U.S. Navy Manufacturing Technology Program on Ion Implantation," Materials Science and Engineering, 90(1987) pp. 385-397. These workers have noted, inter alia, that sputtering is an effect which must be taken into consideration for high fluence ion implantation. They have specifically noted that the "sputtering yield" depends on the energy deposition function, the escape depth for a sputtered ion, and the binding energy to the surface. They have also noted that the sputtering yield is a function of the angle of incidence of the ion beam on the sample. One of the consequences of this angular dependence of sputtering, these workers have observed, is the fact that the retained ion implanted dose at steady state is a function of the geometry of the part being ion implanted.
Recently, certain unexpected advantages have been obtained using a hybrid process designated as ion-beam-assisted deposition (IAD), also referred to as ion-beam-enhanced deposition (IBED). See R. A. Kant et al, "Ion Beam Modification of TiN Films During Vapor Deposition," Materials Science and Engineering, 90(1987), pp. 357-365. In this hybrid process, a sample is provided with layers of coatings by reactive vapor deposition while at the same time the deposited layers are also exposed to bombardment by energetic ions of an ion beam. Some of these unexpected advantages have included a reduced oxygen contamination in the deposited layers of coatings, a broader coating-substrate interface, larger grains and increased lattice constants in the deposited layers of coatings, with the coatings being both denser and more adherent than conventionally prepared coatings without simultaneous ion bombardment. Additionally, the hybrid process allows for the production of considerably thicker layers of similar composition and structure to those obtained by direct ion implantation. The hybrid process also permits the fabrication of deposited coatings of unique microstructures, such as amorphous or metastable phases, it extends the range of allowable processing conditions, including deposition at room temperature, and it also provides for ion beam mixing of the coating-substrate interface. The hybrid process also is believed to reduce some of the problems encountered during conventional vapor deposition, namely poor adherence, high porosity and high internal stress prevalent in the vapor deposited layers. The hybrid process requires, however, the concurrent utilization of an ion beam implanter and of a reactive evaporation system, both designed to impact on a sample in a specially designed deposition chamber. The process is thus both expensive and cumbersome.